Electric fuse



Dec. 24, 1929. T. E. MURRAY v1,740,699

l ELECTRIC FUSE Filed Feb. 7, 1 928 wuemtoz 'o/w15 Ef MHRA r.

Patented Dec. 24, 1929 uNilri-:o STATES y PATENT" oFl-ICE- THOMAS E.MURRAY, OF BROOKLYN, YORK; JOSEPH BRADLEY MURRAY, THOMAS E. MURRAY, JR.,AND JOHN F. MURRAY, EXECUTORS SAID THOMAS E. MURRAY,

- 'DECEASED ELECTRIC FUSE The invention aims to provide certainimprovements in fuses designed particularly for high voltages butapplicable also for ordinary Fig. 3 is a vertical section ofamodiii-ca-Y tion.

Fig. 4 is a similar-section of another modi fication.

.Referring to the drawings the `fuse strip'or element 1 is provided atan intermediate point in its length with a portion 2 of reduced crosssection to form a localized blowing oint. Near the blowing point,according to Figs. 1 and 2, are heads or plungers 3, one on each side,separated from each other Iby a slight space. Theseplungers are adaptedtok move freely in a cylinder preferably composed of an inner insulatingtube 4 of fibre and an outer tube 5 of stronger material such as iron orsteel to withstand the force of the explosion. The heads 3 may be ofber, heattreated wood or other suitable material. When the fuse Ablowsor burns out at the narrow part 2, the (gas vgenerated therein willseparate the hea s 3 forcibly and ly forcing one or both of them sorapidly out of the open ends of the tube that any arc formed at theblowing point will be unable to follow the widely separated parts of thefuse strip. The strip'may be fastened in the plungers 3 in any suitableway. For greater security they may be bent as at 6, Fig. 2, be-

- fore being imbedded in the heads. The outer portions may be curved asat 7 to vyield more easily to the force of the explosion.

v The chief diiiicultyinvolved in the use of fuses on high voltagecircuits isa tendency of the current to form and retain an arc betweenthe burned ends of the fuse, with generation of large quantities of gas.The imbedding of the ends of the sections in the romptheads or plungersas shown diminishes the dangerous possibilities in this direction. Thearc will not follow the fuse strip for any substantial distance into theheads. Particularly will it be stopped by .the crooked direction of thefuse strip in the head as shown in Fig. 2. Furthermore the location ofthe heads 3 in the cylinder 4 produces a piston or plunger effect and aWide separation of the ends of the strip after a blow and thus furtherreduces the chance of'establishing or maintaining an arc.

In a previous patent of Thomas E. Murray,

Jr., No. 1,120,226, dated December 8, 1914,

a fuse is shown so arranged that the as generated upon a blow will forcethe en s of the two sections apart. A similar operation is o btained inthepresent case, with the addition of the heads 3 with a confined spacebetween them which will cause the gas pressure to throw the headsviolently apart, and with the additional protection provided by theimbedding of the ends of the broken strip in the heads, and particularlythe crooked shape of the strip in such heads. y

The space for confining the gases may be .closely restricted, as in theMurray patent referred to above; or the clear space bet-Ween the heads 3may be somewhat greater, as in the present drawings, equal to orslightly in excess of the length of the restricted portion of the fusestrip, giving more room' for the generation of gas.

The tube in Fig. 1 is carried on the to of a post 8 of insulatingmaterial. The use strip passes up from terminals 9 at the bottom of thepost, to the top of the same and around and into the open ends of thetube 5. Thus, we have a repulsion effect between the two parts lO-and 11of the fuse or conductor on opposite sides of the porcelain or othernon-conducting post 8 as described in a atent of Thomas E. Murray,` Jr.,No. 1,0 3,619 dated September 23, 1913, which itself tends to throw theends of the fuse apart when the reduced portion thereof burns through.In addition, we have plenty of room for the heads or pistons when theyare thrown apart. The apparatus is carried in a case with a bottom12,side walls 13 and top 14 which may be of wood, for example, andplates 15 of wood are located on the inside in position to receive theblow of the expelled plungers 3 with metal reinforcing strips 16 on theoutside. When a blow occurs the pistons and the ends of the fuse will beblown out against the parts 15 and to approximately the positionsindicated in dotted lines; thus effecting a quick and Wide separation ofthe ends of the fuse. l/Vith such an arrangement on a 15,000 voltcurrent of 25 cycles, using a 200 ampere fuse, I have opened the circuitin from three to iive cycles; the tube in this case being two andone-half inches in diameter and eighteen inches long. And with a amperefuse I have opened the same circuit in half a cycle.

Instead of using two movable heads or plungers 3, a single such plungermay be used, as in Fig. 3, lconlining the gas by a iixed abutment 17 atthe opposite side of the reduced section 2 of the fuse strip. Theabutment 17 is iixed in the upper end of a tube 18 of non-conductingmaterial, the latter being strengthened by a metal cap 19. The lower endof the strip 1 is bent laterally as at 20 to facilitate the easyexpulsion of the plunger with the portion of the strip to which it isattached.

rlllhe plunger does not need to tit tightly in the tube. In Fig. 3,1have illustrated a somewhat greater' clearance than in Fig. 2. rIhecloseness of iit required for practical success depends on the capacityand voltage o1t` the fuse and also on the length oit the plunger. If theplunger is long, the fit need not be so good as when the plunger iscomparatively short. It must be such that the plunger is expelled fromthe tube, carrying with it the attached part of the fuse strip. This aimis facilitated by permitting the plunger to move easily through thetube, and also by the vertical arrangement of Fig. 3 with the plungerbelow thecontracted portion of the strip and with the lower end of thetube open and the strip bentaround out of the vertical line.

With this design, I have obtained satisfactory tests under short circuitconditions at 6600 volts and with fuse capacities up to 100 amperes. Ihave also operated this same gen eral type at 11,000 volts and haveopened short circuit loads the equivalent. of 150,000 kw. These fusesmay, therefore, be used as substitutes for circuit breakers of thecomplicated types now generally thought necessary on lines carryingheavy loads.

The vertical arrangement of Fig. 3 gives this advantage, that the singlemovable lunger is expelled in a downward direction. ut a doubleendedtube, like that of Fig. 1, for example, may also be used efficiently ina vertical position expelling one plunger downward and the other upward.Such an arrangement is shown in. Fig. 4. In addition this figure shows amodification in the shape of the plungers 3. One or both of theseplungers is formed on its inner face with a recess 20. The plungers arebrought face to face. Thus the recesses 20 provide a more limited spacethan is allowed in the previous constructions where such spaces are ofthe full cross section of the plungers. The same method of restrictingthe space may be applied to the other constructions illustrated.

By expelling the plungers, with the ends of the burned fuse, to anunlimited distance the circuit cannot be reestablished, as might be thecase, particularly -on high tension lines, where the ends of the burnedfuse remain within a distance from each other which is limited by theends of the casing. 'Ihe blowing of the fuse fills the space with avapor ot' the metal which is highly expansible and conductive and will,therefore, immediately reestablish tlie circuit if the tension thereinbe great enough to itorm an arc of this gas. rIhis is particularlytrue'where the separated pistons remain in a casing from which the gascannot escape or can escape only slowly.

The space between the plungers or abutments is regulated according tothe character of the fuse metal and the volume of gas which will begenerated. rIlhe plungers will limit the fuse metal gasified to thatportion located betweentheir adjacent faces, with allowance for thegasification of a portion extending slightly into the plungers. Theremust be enough gas generated to move the plungers promptly and swiftlyout of the casing or to a distance Well beyond that 'through which thecalculated volume of gas will carry 10c the current by an arc. Anyexcess or' gas beyond that needed is objectionable because of its highlyconductive character. The movement of the plunger or plungers should besubstantially free so as to oppose no resistance to the explosive elfectof the gas and to permit operation with a minimum quantity of gas.

The space in which the fuse element is exposed is made so slight inproportion to the current carried that the consumption of all the fusemetal in this space is assured. And further consumption beyond thedetermined amountiis prevented by the pistons as above explained, sothat the amount of metal to be consumed is regulated by the length ofsuch space. v

The ends of the case are a considerable distance beyond the plunger.This guides the plungers and gives a prolonged pressure driv- 12o ingthe plungers with an accelerating velocity. It also confines the highlyconductive gas, or metal vapor, for a substantial distancebeyond theblowing point, so as to prevent its spreading to conductorsl at the opposite end of the tube and making a short circuit.

various other modifications than those described may be made by personsskilled in the art without departure from the invention as dened in thefollowing claims.

What I claim is: 'l 1. A fuse comprising anopen-ended case, a plungerwithin said case at a substantial distance from its end, an abutment, afuse element engaged by said plunger and having a blowing point betweenthe abutment and the plunger so that the gas generated by the blowing of,the fuse isconiined, the case being unobstructed vfrom the plunger`tothe end of the case so that the plunger withits engaged portion of thefuse element ismoved promptly and swiftly away from the blowing pointand is permitted to mgve freely through `the case and out of the/openend thereof when the fuse blows. v 2. A fuse comprising a case open atopposite ends, plungers within said case, av fuse element engaged bysaid plungers and having a blowing point between them sc thatthe gasgenerated by the blowing of the fuse is confined between said plungers,the case being unobstructed from 'the plungers to the ends of the caseso that the plungers with their engaged portions -of the fuse element,are moved promptly and. swiftly away from the blowing point and throughthe case and out of the open ends thereof when the fuse blows.A

3.- A fuse comprising a case, a fuse element having a blowing point, aplunger in which the portion of the fuse element near the'blowing pointis encased and an abutment 'separated from the face of said plunger by adistance less than the diameter of the plunger permit the plunger tomove freely through f t e and out of the case on the blowing'o fuse.k v

' .4. A fuse comprising an open-ended case,

. to .move freely throughthe lcase and out of a plunger within saidcase,an abutment, a

fuse element engaged by said plunger andv having a blowing p ointbetween the abutment andthe plunger vso that the-gas generated by thevblowing of the fuse is confined and the plunger, with its engagedportion of the fuse element, is moved promptly and swiftly away from theblowing point and is permitted the open end thereof when the fuseblowsand areceptacle for the blown plunger outside of said case. l

5. A fuse for opening wan electric circuit, comprising a fuse elementhaving a blowing point, means whereby the blowing of the fuse willdisplace the ends of the fuse element adv j accnt tothe blowing point tosuch a distance that .the circuit cannot beA re-established by --thepassage of the current through the gas generatedy and'means forconfining suchgas tity of gas.

`v for a substantial distance beyond the blowing point of thefuse.

6. A fuse for opening an electric circuit, comprising a fuse elementhaving a blowing point, a plunger engaging the fuse element near theblowing point, means for displacing said plunger with'its portion of thefuse element upon the blowing of the fuse to such a distance that thecircuit cannot be re-established by the passage of the current throughthe gas generated, andmeans for confining such gas for a substantialdistance beyond the blowing pointof the fuse.

-7. A fuse comprising a case, a plunger within the case, .an abutment,afuse element engaged by said plunger and having a blowing Vpoint betweenthe abutment and the plunger, the portion of the fuse element betweenthe abutment and the plunger being restricted so that the gasificationthereof will be just suilicient to move-the plunger prompt- `ly andswiftly away from the blowing point to such a distance that the circuitcannot be re-established by the passage of the current throughv the gasgenerated, the movement of the plunger being substantially free so as torequire the generation of a' minimum quan- 8. A fuse comprising a case,a plunger withinsaidcase, an abutment, a fuse element engaged by saidplunger and having a blowing point between the abutmentand the plunger,the movement of the plunger being substantially free and the explosiveeffect of the gas generated by the blowing of the fuse beingsubstantially unresisted so that when.

the fuse blows'the plunger with its .engaged portion of the fuse elementis moved promptly and swiftly away from they blowing point o such adistance that the circuit cannot be liet-established by the passage of,the current t`` rough the gas generated.

9. The fuse of claim 1, the pistonand the abutment being face',l to facewith a recess in one of them-in which the blowing point of 'the fuseelement lies. A 10. A fuse forautomatically opening an electric circuitcarrying a h igh tension c urrent andmeans for automatically displacingthe burned ends of the fuse element on the blowing of the. latter tosuch a distance as to prevent the rea-establishment of such current,

through a considerable distance during Asuch displacement. g

11. A fuse comprising `a fuse element, a l

plunger in which the fuse element is partly encased'andan abutmentseparated from the and means for guiding the displaced ends the amountof metal to be eonsumedis regulated by the length of said space.

12. A fuse comprising an open-ended case, a plunger within said ease, anabutment, a fuse element engaged by said plunger and having a blowingpoint between the abutment and the plunger, the plunger being held inposition by the fuse element alone so that.

the gas generated by the blowing of the fuse is confined and, when thefuse blows, the plunger with its engaged portion of the fuse element ismoved promptly and swiftly away from the blowing point and out. of theopen end of Jche ease. v

In witness whereof, I have hereunto signed my name.

THOMAS E. MURRAY.

